Oral anticoagulant drugs have improved the prognosis of patients with thromboembolic disease. However, optimal oral anticoagulation control is usually hampered by significant interindividual variability coupled with a narrow therapeutic window. In the elderly, this variability is enhanced by concurrent medications, nutritional status and physical condition. Age itself correlates with increased severity of complications, and adverse events due to anticoagulant drug are thought to be responsible for up to 5000 deaths a year in France.